Interference Effect For Galloping And Aerostatic Stability Of Catwalk-main Cable Of Suspension Bridge During Construction

Under the action of strong wind, it is found that vibration amplitude of the main cable of some suspension bridges varies greatly during construction. Vibration amplitude of the main cable has seriously influenced construction period. The galloping instability may be happen because the cross section of main cable during construction is not circular section of completed bridge status. It has the impact on aerostatic coefficients of spire-type main cable of suspension bridge considering aerodynamic interference effect of catwalk during construction. It could further affect properties of the galloping for main cable. The main work and achievements are as follows:1. The numerical simulation method of CFD is used in this paper. The design parameters of catwalk and the main cable of a suspension bridge are adopted. Firstly, referring to the results of wind tunnel experiment for catwalk, validity of the method of parameters’ settings for numerical simulation is verified. Secondly, the drag and lift coefficients of triangles, pentagons and spires shape main cable during construction are calculated, considering the aerodynamic interference effect of catwalk or not. In the end, the galloping coefficients of main cable for different working conditions are calculated by the Deng-Hato criterion during construction. Results show that the drag coefficients of triangle shape main cable for different working conditions decrease continuously during construction, with the increase of cable strand considering aerodynamic interference effect of catwalk, but the lift coefficients are opposite. The drag coefficients of pentagons shape main cable for different working conditions increase continuously during construction, with the increase of cable strand considering aerodynamic interference effect of catwalk, but the lift coefficients are opposite. The drag coefficients of spires shape main cable for different working conditions increase continuously during construction, with the increase of cable strand considering aerodynamic interference effect of catwalk, but the lift coefficients are opposite as a whole. Through comparing the catwalk existing or not, when taking into account the aerodynamic interference effect of catwalk, the drag and lift coefficients of the main cable during construction are both reduced. In addition, when the galloping coefficients of different working condition are calculated, aerodynamic interference effect of catwalk cannot be ignored.2. The result of this study indicates that galloping instability may occur because of the transient main cable of a long-span suspension bridge during construction. However, the erection of the main cable of a long-span suspension bridge is semi-surrounded by the catwalk during construction.Thus, variation of parameters of catwalk’s design has an enormous effect on the galloping stability for main cable during construction. In order to make a research for influence of parameters of catwalk’s design on a spire-type main cable for galloping during the construction of a suspension bridge, results of wind tunnel test for catwalk are used as references. The spire-type main cable of a long-span suspension bridge under different working conditions during construction is selected as the research object. the CFD software FLUENT is used. The validity of the numerical analysis model is confirmed by combining the results of the wind tunnel test on catwalk aerostatic coefficients. The aerostatic coefficients of the spire-type main cable under typical working conditions which are the condition of space from surface layer for catwalk to the bottom of main cable、height of catwalk、width of catwalk、ventilation rate of side mesh of catwalk and ventilation rate of bottom web of catwalk. In the end, Deng-Hato criterion is applied to analysis of galloping for parameters of catwalk’s design during construction. Firstly, the results indicate that parameters of space from surface layer of catwalk to the bottom of main cable、catwalk’s width and catwalk’s height has little influence on drag coefficients of the main cable during construction, but the lift coefficients increase. Parameters of 84 cm for the space from surface layer of catwalk to the bottom of main cable、4.5m for the width of catwalk and 1.3m for the height of catwalk are more favorable for the galloping instability prevention. Secondly, the drag coefficients of main cable decrease during construction by ventilation rate of side mesh of catwalk, but the lift coefficients perform irregularly. 50% for ventilation rate of side mesh of catwalk is more favorable for the galloping instability prevention. Thirdly, the variation for ventilation rate of bottom web of catwalk is more sensitive to the drag coefficients and lift coefficients. 70% for ventilation rate of bottom web of catwalk is more favorable for the galloping instability prevention. Fourthly, design parameters of galloping instability of the main cable occur minimal possibility are that 84 cm for the space from surface layer of catwalk to the bottom of main cable、4.5m for the width of catwalk、1.3m for the height of catwalk、50% for ventilation rate of side mesh of catwalk and 70% for ventilation rate of bottom web of catwalk.3. Considering aerodynamic interference effect between main cable and catwalk of a long-span suspension bridge during construction, both aerodynamic stability and aerostatic stability have constant changes with the increase of cable strand during construction. In order to make a study for influence of main cables of a long-span suspension bridge on aerostatic stability of catwalk during construction, results of wind tunnel test for catwalk are used as references. The main cable and catwalk of a long-span suspension bridge under different working conditions during construction are selected as the research object. Firstly, the validity of the numerical analysis model is confirmed by combining the results of the wind tunnel test on catwalk aerostatic coefficients. Secondly, the three-component coefficients of catwalk for different working conditions during construction are calculated by the former verified method. In the end, considering the geometric nonlinearity of the catwalk and wind load, we do research of aerostatic stability of catwalk under different working conditions for main cable during construction by secondary development of ANSYS. The results indicate that when taking into account the influence of spire-type main cable during construction, it will show that drag coefficients and torque coefficients increase firstly, and then they will reduce. Lift coefficients reduce within the scope of negative wind angle of attack firstly, and then they will increase. Within the scope of positive wind angle of attack, lift coefficients almost have no change. With the construction of spire-type main cable, the critical wind velocity of instability reduce, and then it will increase. In the finished bridge stage, critical wind velocity of instability becomes small again. The critical wind velocity of instability of 15# working condition is close to inspection wind velocity of aerostatic stability at 10 m height during construction and finished bridge state. It should be paid attention to strengthen the observation during construction. When it is necessary, measures of wind resistance should be taken for safety.